1. Field of the Invention
This invention relates to a hybrid type drive unit including an engine and an electric motor both mounted on a vehicle (e.g., a hybrid type motorcycle) and selectively used for driving one or more drive wheels.
2. Description of the Related Art
Conventionally, vehicles such as motorcycles and automobiles typically have an engine for driving one or more wheels thereof. Recently, vehicle manufacturers and the consuming public have become more sensitive to environmental issues. It is thus desired to reduce carbon dioxide discharged from vehicles powered by an internal combustion engine or to reduce substances which give rise to the pollution of the environment. Accordingly, developments have been made in connection with vehicles having a drive motor which drives a wheel(s) together with an engine, i.e., so-called hybrid vehicles.
A hybrid vehicle can be a parallel type hybrid vehicle in which a drive wheel(s) is alternatively driven by an engine and a drive motor in response to, for example, a running condition of the vehicle or the amount of power remaining in a generator-charged battery. A hybrid vehicle can also be a series type hybrid vehicle in which an engine drives a generator, which in turn drives a drive motor for driving a drive wheel(s) using the electric power generated by the generator.
One example of a drive unit of the parallel type hybrid vehicle (particularly, four wheeled vehicles) is disclosed in Japanese Patent Publication No. JP 2000-343964.
The drive unit disclosed in JP 2000-343964 includes an engine, a generator, a power distributing mechanism for distributing the drive power of the engine between the generator and drive wheels, and an electric motor for driving the drive wheels with the electric power of the generator. In the vehicle of JP 2000-343964, the engine, the generator, the power distributing mechanism and the motor are coaxially arranged in a transverse direction of the vehicle.
More specifically, in the drive unit of JP 2000-343964, a power transmitting shaft coaxially disposed with the crankshaft is coupled with an end of the crankshaft through a clutch. The power transmitting shaft extends through the generator to define an axis of a planetary gear set of the power distributing mechanism, which includes a sun gear and a ring gear. The power transmitting shaft also extends through the motor. The power transmitting shaft thus can be the longest and the thinnest member in the structure of the drive unit. Additionally, the power transmitting shaft is connected to a planetary gear carrier supporting planetary gears for rotation, while the power transmitting shaft extends through the power distributing mechanism.
It is desired that such a conventional hybrid type drive unit be mounted on a motorcycle. However, space for mounting the drive unit on a motorcycle is limited to a portion of the vehicle body located between a front wheel and a rear wheel and below a seat. In addition, generally, a motorcycle has a narrower width than an automobile. The mounting space thus can be further limited. Accordingly, it is extremely difficult to provide the motorcycle with the drive unit that has the arrangement in which the engine, the generator, the power distributing mechanism and the motor are arranged coaxially and in series. As a result, no motorcycle has been developed in which the drive unit constructed as discussed above is efficiently mounted.